Negative resistance pulse generator



Jan. 1, 1952 Q GUTHRlE 2,580,423

NEGATIVE RESISTANCE PULSE GENERATOR v Filed May 29, 1943 2 SHEETS-SHEET l Iii-5&1-

8/45' SUPPLY o I1LE=E R. (LGUTHRIE I Mm Jan. 1, 1952 R. c. GUTHRIE NEGATIVE RESISTANCE PULSE GENERATOR 2 Sl-IEETS-Sl-IEET 2 Filed May 29, 1943 T IME"'- Liz-=4 3mm RC. GUTHRHE Patented Jan. 1, 1952 UNITED STATES PATENT OFFICE NEGATIVE RESISTANCE PULSE GENERATOR Robert C. Guthrie, Washington, D.

Application May 29, 1943, Serial No. 488,971

(Granted under the act of March 3, 1883, as

8 Claims.

This invention relates to a novel negative resistance device comprising a multiple grid vacuum tube which is designed to operate independently of secondary emission as employed by the dynatron and deviates from the negative transconductance action of the transitron" through the utilization both of retarding e1ec trostatic fields between the tube elements, and degeneration. This invention also relates to a novel means for producing a series of controllable phase and time length energy pulses such as those employed for unblocking a pulse receiver of the radio echo type at the proper time so as to receive only the desired energy reflection.

It is an object of this invention to provide a novel means for obtaining a negative slope in the grid voltage-plate current characteristic of an ordinary multiple grid vacuum tube.

It is another object of this invention to provide a novel means for obtaining and controlling a negative slope in the grid voltage-plate current curve of a multiple grid vacuum tube.

It is another object of this invention to provide a means for producing a series of controllable phase and time length energy pulses.

Other objects and features of the present invention will become apparent upon a careful consideration of the following detailed description when taken together with the accompanying drawings the figures of which are designed forv the express purpose of illustration and not as a definition of the limits of the invention. Reference for the latter purpose is to be had to the appended claims.

Fig. 1 is a schematic diagram of a preferred embodiment of the present invention,

Fig. 2 is a graphical representation of a typical grid voltage-plate current curve obtained from the multiple grid vacuum tube l contained in Fig. 1,

Fig. 3 is a graphical representation of a typical input voltage to tube I, and

Fig. 4 is a graphical representation of typical input and output voltage wave forms of tube 2 in Fig. 1.

It is contemplated by the present invention to provide a means for producing a negative slope in the grid voltage-plate current curve of an ordinary multiple grid tube. It is also contemplated by the present invention to provide a means for producing a controllable phase, substantially square output pulse from a linearly varying input voltage.

amended April 30, 1928; 370 O. G.'757) of my novel negative resistance device comprising the multiple grid tube I and associated circuits. The control grid 3 affords a suitable input connection to the tube by way of lead 20 and also a connection to a bias supply by way of resistances l2 and i3 and potentiometer [4 across which a bias voltage is connected. The suppres-. sor grid 1, like most tubes of this type is tied to the cathode II) which in turn is connected to ground by way of a single resistance ll. Grids 4 and 6 are tied together and connected to a source of positive potential of somewhat lower magnitude than that connected to the plate 9,

while the grid 8 may be connected to ground, a source of negative potential or even to a source:

of small positive potential say in the order of one or two volts.

A more complete understanding may be had of the present invention upon careful consideration of the following discussion when read in conjunction with Figures 1 and 2. The change in control grid voltage of the tube I is shown in Fig. 2 and laid out along the abscissa as taken with respect to ground. Thus as the control grid 3 is driven in a less negative direction, from say cut-oil, the plate current will increase in a man ner common to the ordinary amplifier, i. e., as the grid voltage is increased the plate current undergoes a corresponding increase since the voltage on the cathode I0 due to the IR drop across resistance II will lag behind the rise in grid 3 voltage until maximum plate current is reached. At this point the voltage difference and conseouently the electrostatic field between grids 3 and 4 is such that an increase in potential on grid 3 will merely operate to retard the electrons. Thus as grid 3 is driven further positive some of the electrons are collected by the grid 4 while some escape through the grid-4 meshes and are repelled by the low potential grid 8, while others I are colleceted by grid 6 and still others pass Reference is had more particularly to Fig. 1

wherein there is shown a preferred embodiment through grids 8 and 6 to be collected at the plate 9. Thus grid 4, which I will hereinafter call the anode in view of its function in the tube, now draws considerable current. As the control grid 3 is driven still further positive, more and more of the electrons which escape from the cathode are collected by grids 4 and 6, and are repelled by grid 8, so that less and less are collected by the plate 9. The anode 4 current which flows through the cathode circuit produces an (IR) drop across the resistance H to drive the cathode further positive with respect to the grid 8 until this grid acts to finally cut off the plate current flow. It, therefore, becomes apparent that by 3 driving the control grid 3 through a finite range of potentials a plate current characteristic with respect to grid voltage similar to Fig. 2 can be obtained. It follows that by the proper biasing of In pentode operation the cathodeisagain connected to ground by a single resistance, the sup pressor grid directly to ground, the screen grid to a source of fixed positive potentialioi somewhat lesser magnitude than the plate potential, and the control grid to a source of bias supply and an input voltage. The primary reason for arbitrarily selecting the potential on grid 8 is that the potential on this griddetermines to a certain extent the maximum. value ofv plate current and. the control grid voltage at which.v it will occur.. since-the. more, negative this grid, is made the smaller number. of electronsare allowed to escape to thejplate and consequently. requires less re- 7 tarding actionbetween.control gridit and. anode.

4Iin order to obtain. the. desired characteristic.

Reference is again. had. to Fig. 1- which. also. shows in. detail my. novel pulse. generator comprising tube. l. and. 2'. connected. in cascade. For. the purpose of. settingv forth this invention. in better light let itbe assumed that a. saw-tooth. wave according to.Fig.-.3 is being iedinto tube I. An input voltage of this. type canbe readil used. when the. present invention. is incorporated. with. aradioecho pulse receiver of the class described. above. The bias on grid 3 is adjusted by potentiometer M. sothat griddle driven. through the conducting region, i. e. from below. thelower cutoff value toabove theupper cut-off value. Thusv as. the; grid is driven through the. conducting region. of the. tube. a negative. and. approximately parabolic pulse similar t .A.inFig,-.4. is--.p1 .oduced; in; the. output circuit. oftube I. A. better. understanding of theproduction. of. thispulse, may be obtained. from Fig. 3: which. shows; clearly, the. saw-tooth input. voltage swinging. through. the. conducting region oftube. IV as representedrby the two. parallel lines g, andh. The. width. of. this. pulsewith respectto the saw-toothwave is.ex.-

aggerated considerably. for purposes oifcl arityh,

Obviously potentiometer It. can. be. regulated to. vary, the voltage. level aboutwhich. the input voltage. swings thereby shifting. the time phaseoi.

occurrence of. the. negative output. pulseesshown.

by the dotted. and solidcurvesin'JI-ig. 8;.

'Eheoutput of. tube l iscoupled'. to the controlelectrode of tubev 2,. which; is. also connected through'resistances. it and. l 6 tea source of'positive. potential, but. may bev connected to ground if. desir.ed.1 Triodei. isbiased to draw a. heavy platecurrent. by. way or the. self'biasin'g circuit. comprisingthe. variable cathode resistance 58 shunted by a large capacitance. l9. which operates. to maintain.the.bias constant. for rapid. variation. in. input potential. As. the. leading. edge of the parabolic output... pulse of tube i drives grid 2i. ina negative directionthereis no. immediate reductioninplate current since. condenser Midischarges simultaneously to maintain theyoltage difierence betweencathode ll andgrid 2i constantu After grid=.2ll is driven negative topointa asshowninv curve A oi l ig. l, which exceeds the iii) cut-off is reached at point b. The tube will then remain at'cut-ofi over the zero slope of the input voltage as shown in curve A as extending from points I) to 0 until the grid is driven less negative from c to d to cause plate current to flow again and. thereby recharge condenser. It and thus resume normal bias on the tube. The further driving of grid 2| in a less negative direction merely causes rectified grid current to flow and thus results in a further charging of condenser I9 to compensate for the" less negative grid voltage. It, therefore, becomes apparent that the effective input voltage" to tube 2 is shown in curve B of Fig. t which obviously produces an output voltage according to curve C. Thus if resistance It is properly regulated the effective time of charge and discharge of. condenser l9 can be varied to regulate the spacing'between the dotted lines e and f and consequently a relative time length and amplitude adjustment of the output pulse willresult.

Although Ihave shown and described only cer-- tainand specific embodiments of the present invention, I am fully aware of the many modifications possible thereof. Therefore, this invention is notto be restricted except insofar as is necessitated'by the prior art and the spirit of the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of' America for governmental purpose without the payment of any royalties: thereon or therefor.

I claim:

1. The'combination of; a vacuum tube'having at least a plate, a cathode, a screen grid, a control grid and one other plate current control electrode between the screen grid and the plate, means" applying fixed operating potentials to said screen and plateelectrodes, an unbypassed resistor re"- turning said cathode to ground for causing the" cathode potential to follow the signal variations applied to the control grid, signal input means coupled to said control grid for delivering large. positive signal voltage variations thereto, and

means returning said other plate current control electrode to a point of potential negative of the cathode whereby increases in cathode potentials cause a decrease in plate current.

2; A means for producing an energy Dulsecomprising, anelectron tube having anode, cathode and grid electrodes; means providing said. tube with an inflection point in its transconductancei characteristic, said inflection point beingbounded on one side with. a positive transconductance re:- gion andon the other side with a negative transconductance region, an output circuit. coupled to the anode of said tube, and signal input means: coupled to the grid electrode of said tube for sweeping the operatingpoint of said tube'across the inflection point of said transconductance characteristic. whereby an impulse is formed in the output circuit of said tube.

3. A means for producing an energy pulse comprising, an electron tube having anode, cathode, and gridelectrodes, means providing said tube with an inflection point i its transconductance characteristic, said inflection point beingbounded by a-pcsitive,transconductance region on oneside thereof and a negative transconductance region on the other side thereof, anoutput' circuit coupled to the anode of said tube, means statically, biasing the operating point of said'tube to one side, of .the'inflection point of saidtrans conductance characteristic, and a sawtooth sigha! input means coupled to the grid electrode of said tube to sweep the operating point of said tube across the inflection point of said transconductance characteristic whereby an impulse is formed in the output circuit of said tube.

4. A means for producing an energy pulse comprising, an electron tube having anode, cathode, and grid electrodes, means providing said tube with an inflection point in its transconductance characteristic, said inflection point being bounded by a positive transconductance region on one side thereof and a negative transconductance region on the other side thereof, an output circuit coupled to the anode of said tube, means statically biasing the operating point of said tube to one side of the inflection point of said transconductance characteristic, and a sawtooth signal input means coupled to the grid electrode of said tube to sweep the operating point of said tube across the inflection point of said transconductance characteristic whereby an impulse is formed in the output circuit of said tube, and means regulating the biasing of said operating point to control the time occurrence of said impulse relative to the initiation of said sawtooth signal.

5. A means for producing an energy pulse comprising, an electron tube having anode, cathode, and grid electrodes, means providing said tube with an inflection point in its transconductance characteristic, said inflection point being bounded by a positive transconductance region on one side thereof and a negative transconductance region on the other side thereof, an output circuit coupled to the anode of said tube, means coupled to the grid electrode of said tube sweeping the operating point of said tube across the inflection point of said transconductance curve whereby an impulse is formed in the output circuit of said tube, and limiting means coupled to said output circuit operative responsive to the output of said tube for shaping said impulse.

6. A means for producing an energy pulse comprising, an electron tube having anode, cathode. and grid electrodes, means providing said tube with an inflection point in its transconductance characteristic, said inflection point being bounded by a positive transconductance region on one side thereof and a negative transconductance region on the other side thereof, an output circuit coupled to the anode of said tube, means coupled to the grid electrode of said tube operative to sweep the operating point of said tube across said inflection point of said transconductance characteristic whereby an impulse is formed in the output circuit of said tube, limiting means coupled to said output circuit operative responsive to the output of said tube for shaping said impulse, and means incorporated in said limiting means for selectively controlling the duration and amplitude of the output thereof.

7. The method of generating a voltage pulse in the plate circuit of a grid controlled vacuum tube having an inflection point in its transconductance region, said inflection point being bounded on one side by a positive transconductance region and on the other side by a negative transconductance region, which comprises, biasing said tube for operation on one side of said inflection point, and then rapidly shifting the operational point of said tube from said one side of said inflection point to the other side thereof to thereby produce a momentary pulse of current in the plate circuit of said tube.

8. The method of generating a voltage pulse in the plate circuit of a grid controlled vacuum tube having an inflection point in its transconductance region, said inflection point being bounded on one side by a positive transconductance region and on the other side by a negative transconductance region, which comprises, biasing said tube for operation on one side of said inflection point, rapidly shifting the operational point of said tube from said one side of said inflection point to the other side thereof to thereby produce a momentary pulse of current in the plate circuit of said tube, and then converting said momentary pulse of current into a substantially rectangular voltage pulse.

ROBERT C. GUTHRIE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

